If you already know your ring size you can skip this step.
The difference between a comfortable and uncomfortable ring is only a few tenth of a mm so it’s important you get your ring size right. If you aren’t going to wear your ring all of the time you can probably get by with getting a nearly close measurement. Try to measure your finger when you are warm, your overall ring size will be at it’s largest then.
Option 1: Go to a jewelry store
For absolutely best result go see a jeweler and ask them to measure your ring finger. Ask them to use a “Wide Band Ring Gauge”, if they use a thin gauge tool it wont be ideal as it wont truly represent the width of the NFC Ring.
Option 2: Purchase a tool to measure at home
Second best option to is to spend a ~5 dollars on a finger size gauge, such as this one.
Option 3: Use a web based tool to measure your finger width
Warning: This is extremely experimental
We provide a web based tool that uses your webcam and a card magnetic strip to measure the width of a finger and suggest a ring size. It is extremely experimental and should only be used as a last resort.
Secretly measuring someones ring size
Your best bet here is to ask them to hold a magnetic strip from a membership or credit card in their hand and take a picture on a high resolution camera. You can then use the magnetic strip as a reference point for size (they are all a standard width) and do some basic math to figure out the width of the finger. Add 20% to the overall size in MM for comfort.